the single most important criteria when replacing Github
Consider all the data that's used to provide the value-added features on top of git. Issue tracking, wikis, notes in commits, lists of forks, pull requests, access controls, hooks, other configuration, etc.
Is that data stored in a git repository?
BTW, I can't tell you how relieved I am to click on those LWN links and see that they're not stories that I wrote and have forgotten about. That sort of thing happens, let's say, "not rarely."